1. Field of the Invention
This invention relates to a method for arc welding aimed at improving the bevel profiling performance by an arc rotating at an elevated speed.
2. Description of the Prior Art
The method for arc welding wherein an electrode wire is revolved to cause an arc to be rotated at an elevated speed to effect welding is known, for example, from the Japanese Laid-Open Patent Publication No. 133871/1980. This welding method may be advantageously applied to narrow bevel welding or to fillet welding since the physical effect such as the arc force or heat may be uniformly distributed around the welding pond due to the high speed arc rotation to promote the curvature or smoothing of the weld bead or penetration into surrounding portions.
Furthermore, as disclosed in the Japanese Laid-Open Patent Publication No. 91877/1982, the above method for arc welding may be adapted to automatic bevel profiling with high response characteristics since the arc voltage or current waveform produced during the high speed rotation of the arc may be separately integrated at the left and right sides in the proceeding direction of welding and the offset voltage thus obtained may be directly used as the input to the driving electric motor to effect servo drive or control. In this manner, in addition to the above described advantage in connection with the formation of weld beads, there is obtained an additional advantage that the electrode terminal position can be set with high precision during welding.
On the other hand, the so-called arc sensor system in which the current or voltage waveform of the welding arc is used as the bevel profiling sensor, is also well-known not only in connection with the above described method for arc welding in which the arc is rotated at an elevated speed, but also in connection with a welding method in which the electrode is linearly reciprocated along the width of the bevel, as disclosed, for example, in the Japanese Laid-Open Patent Publications Nos. 19445/1979 or 26261/1979.
In the above arc sensor system, the higher the rotational speed or the speed of oscillation, both expressed in Hz, of the arc, indicating the number of revolutions or the number of times of oscillations of the arc per unit time (second), the more excellent the detection or control capability of the arc sensor.
However, in the welding method of the aforementioned linear oscillation system, the speed of arc oscillation cannot be elevated excessively because of mechanical constraint, so that a practical limit is set to about 5 Hz. Thus a limit is set to the resolution as the arc sensor, such that it is difficult to improve the control accuracy and detection capability further.
With the welding method in which an arc is rotated at an elevated speed, a rotational speed of the order of 100 Hz, for example, can be produced easily to improve the detection and control capability of the arc sensor further so that the method is better than the welding method of the linear reciprocation system.
However, in the above welding method in which the arc rotated at an elevated speed is used for welding, when the rotational speed of the arc is lowered incidentally, a definite offset voltage cannot be obtained by separately integrating the arc voltage or current waveform on the left and right sides relative to the proceeding direction of welding. The result is that the effect of the noise presents itself so pronouncedly that it is not possible to satisfactorily exhibit the effect of the arc sensor.